First Pharyngeal Arch

The first pharyngeal arch consists of a dorsal portion, the maxillary process, which extends forward beneath the region of the eye, and a ventral portion,

Branchial Arches
Figure 15.3 Development of the pharyngeal arches. A. 25 days. B. 28 days. C. 5 weeks.
Thyroid Gland Arch
Figure 15.4 Pharyngeal pouches as outpocketings of the foregut and the primordium of the thyroid gland and aortic arches.

the mandibular process, which contains Meckel's cartilage (Figs. 15.5 and 15.8A). During further development, Meckel's cartilage disappears except for two small portions at its dorsal end that persist and form the incus and malleus (Figs. 15.8B and 15.9). Mesenchyme of the maxillary process gives rise to the premaxilla, maxilla, zygomatic bone, and part of the temporal bone through membranous ossification (Fig. 15.8B). The mandible is also formed by membranous ossification of mesenchymal tissue surrounding Meckel's cartilage. In addition, the first arch contributes to formation of the bones of the middle ear (see Chapter 16).

Musculature of the first pharyngeal arch includes the muscles of mastication (temporalis, masseter, and pterygoids), anterior belly of the digastric,

Stomodeum Weeks

Frontonasal prominence

Maxillary prominence "U Stomodeum

Frontonasal prominence Nasal placode

Maxillary prominence

Mandibular arch

Pharyngeal arches, 2nd and 3rd

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